The accurate measurement of orifices and passageways in the human body is important for the success of a variety of medical procedures. In particular, accurate measurement of the anatomy of the human body is often crucial for the successful implantation of prosthetic devices. For example, in selecting a prosthetic heart valve, it is preferable to select the largest size valve possible. A large effective valve orifice is preferable because it creates less resistance to forward flow and requires the heart to do less work.
Traditional sizing of a heart valve annulus is performed by placing a known diameter sizing apparatus into the annulus and observing the fit of the sizing apparatus. If the sizing apparatus appears to fit easily into the annulus, the sizing apparatus is retracted and a larger sizing apparatus is inserted. In some procedures, the native annulus is expanded from its natural state due to the radial outward pressure of a prosthetic valve implanted within the native annulus. Unfortunately, known sizing apparatuses do not take into consideration the final, functional size of the annulus when expanded by the prosthetic valve. That is, these techniques cannot measure the size of a heart valve annulus when it is expanded under pressure.